1. Field of the Invention
Example embodiments relate in general to a method and apparatus for the mechanical repair of a Boiling Water Reactor (BWR) jet pump restrainer assembly. Specifically, example embodiments relate to mechanical repair of a potentially damaged contact area on either an inlet mixer wedge or a restrainer bracket of a restrainer assembly used to horizontally support a jet pump assembly against riser piping to reduce vibration.
2. Related Art
BWRs are designed to generate steam in reactor pressure vessels (“RPVs”) by heating the water surrounding uranium-containing tubes of fuel assemblies located in the RPV core regions. The RPVs have recirculation loops designed to facilitate the circulation of water in the core regions. The recirculation loops generally include large centrifugal pumps that pump water out of the RPVs and return the water to the inlets of jet pump assemblies located in annular regions in the RPVs surrounding the core regions. The jet pump assemblies are designed to entrain the surrounding water in the annular regions and then discharge the water in a manner that induces a desired flow pattern in the core regions.
The jet pump assemblies are subject to vibrations caused by hydraulic forces due to the flow of water and/or by the rotation of the centrifugal pumps. Thus, in one BWR design, the jet pump assemblies are horizontally supported against vibration with a jet pump restrainer assembly including a bracket using a three point suspension system. A three point system generally includes a wedge movably mounted on a vertically oriented guide rod that is attached to a jet pump assembly and extends through the space between the bracket and the jet pump. The wedge, which may weigh about seven pounds, is designed to slide downwardly under the force of gravity into the space between the bracket and the jet pump assembly and thereby urge the jet pump against the adjustment screws.
It has been found that the mating (or seating) surfaces of the wedges and/or the brackets of some commercial BWRs have worn substantially after operation over long periods of time. In some cases, the softer interior metal underlying the hardened surfaces of the wedges have worn extensively. It is believed that the wearing is caused by a fretting type of action when the hydraulic forces and/or pump vibrations induce the wedges to chatter or to rise upwardly and then fall back against the bracket. In addition, it is believed that the jet pump assemblies may move away from the adjustment screws in extreme cases.
The jet pump restrainer assemblies may be repaired by replacing the worn wedges and/or brackets. However, the jet pump assemblies and/or brackets would need to be disassembled, machined and reassembled, and the old parts would need to be replaced.